The present invention relates to an electrophotographic photosensitive member, particularly one characterized by including an intermediate layer containing a specific aluminum compound, a process for producing the photosensitive member, and a process cartridge and an electrophotographic apparatus including the photosensitive member.
An electrophotographic photosensitive member generally has a photosensitive layer on an electroconductive support. The photosensitive layer is generally a very thin layer and is liable to have an uneven thickness due to a surface defect or irregularity, such as damages or attachment, on the support surface. This liability is particularly serious in a currently predominant so-called function-separation type photosensitive layer which includes a charge generation layer having a very small thickness on the order of 0.5 xcexcm and a charge transport layer. As such an ununiformity of photosensitive layer thickness naturally results in potential irregularity or sensitivity irregularity, the photosensitive layer should be formed as uniformly as possible. More specifically, such a potential irregularity or sensitivity irregularity results in images accompanied with black spotty defects (black spots) and fog.
On the other hand, as a measure for providing a sharper potential distribution of electrostatic latent image, there may be conceived of decreasing the photosensitive layer thickness of an electrophoto-graphic photosensitive member. For example, in a lamination type or function separation-type photosensitive member, charges generated in the charge generation layer are injected into the charge transport layer and moved along an electric field to the photosensitive member surface to locally neutralize the surface potential thereat, thereby forming an electrostatic latent image. In this case, if the charge transport layer thickness is reduced to increase the electric field strength and reduce the charge migration distance, the charge diffusion in directions perpendicular to the electric field can be suppressed to provide a sharp electrostatic latent image faithful to exposure light, such as digital laser beam spots. Further, if an electrophotographic photosensitive member is considered as a kind of dielectric member, a smaller photosensitive layer thickness results in a large electrostatic capacitance of the photosensitive member and correspondingly a higher charge density at the photosensitive member surface for providing a prescribed surface potential. As a result, the developing electric field is enhanced and the electrostatic latent image potential distribution is intensified to result in a higher resolution.
However, in a conventional electrophoto-graphic photosensitive member, an increased electric field intensity caused by a smaller photosensitive layer thickness has promoted charge injection from the support side, thus resulting in undesirable phenomena, such as a lower chargeability and so-called fog in the reversal development system. Accordingly, though the photosensitive layer thickness reduction is expected to result in a higher resolution through an improved reproducibility of dots formed by digital exposure light, such as a laser beam, it is also accompanied with difficulties attributable to charge injection, thus leaving a problem for practical application.
For solving the problem, it has been proposed to insert an intermediate layer between the support and the photosensitive layer for the purpose of coating surface defects on the support, improving the adhesion between the support and the photosensitive layer and preventing the carrier injection from the support to the photosensitive layer.
Hitherto, it has been proposed to form such intermediate layers of resins, such as polyamide (JP-A 48-47344 and JP-A 52-25638), polyester (JP-A 52-20836 and JP-A 54-26738), polyurethane (JP-A 53-89435 and JP-A 2-115858), quaternary ammonium salt-containing acrylic polymer (JP-A 51-126149) and casein (JP-A 55-103556). However, an intermediate layer of a material as described above is liable to have an electrical resistance which is liable to change depending on environmental changes, so that it has been difficult to provide an electrophotographic photosensitive member having stable and excellent potential characteristics in all environmentals ranging from low temperature/low humidity to high temperature/high humidity.
For example, in the case where such an electrophotographic photosensitive member is used in a low temperature/low humidity environment liable to cause an increase in resistivity of the intermediate layer, charges are liable to remain in the intermediate layer, thus resulting in increases in light-part potential and residual potential. As a result, the resultant images are liable to be foggy in the case of normal development and are liable to be thinner in image density in the case of reversal development, so that it is difficult to continually obtain images of prescribed image quality. On the other hand, in the case where such an electrophoto-graphic photosensitive member is used in a high temperature/high humidity environment liable to cause a lowering in resistivity of the intermediate layer, the barrier function of the intermediate layer is liable to be lowered, thus resulting in an increased carrier injection from the support and a lowering in dark-part potential. As a result, the resultant images are liable to have a lower image density in the case of normal development and are liable to be accompanied with black spots and fog in the case of reversal development.
JP-A 62-272277 has disclosed to form an intermediate layer by applying a coating liquid comprising a mixture of an organometallic compound, such as a silane coupling agent or a metal alkoxide, in an organic solvent. When such a coating film of an organic solution of a relatively low-molecular weight organometallic compound is subjected to a subsequent drying step, the organometallic compound is hydrolyzed and polymerized to form a cured film having a network structure. However, a cured film obtained through such a process is liable to be cracked at a certain thickness or larger. The resultant crack in the intermediate layer results in a thinner image formation in the normal development or black spots or fog in the reversal development. Accordingly, such an intermediate layer formed by application and curing of a coating liquid obtained by mixing of an organometallic compound in an organic solvent can only be formed in a small thickness. However, such an intermediate layer of only a small thickness is liable to exhibit an insufficient ability of preventing carrier injection from the support to the photosensitive layer, thus also resulting in a lower image density in the normal development and black spots and fog in the reversal development. Accordingly, it is very difficult to satisfy the image quality and potential characteristic in combination. Moreover, such organometallic compounds used for providing an intermediate layer coating liquid, as represented by alkoxides and acetylacetonates of zirconium, titanium and aluminum, are strongly hydrolyzable, and the coating liquid comprising such an orgametallic compound and an organic solvent is liable to cause a precipitate or a viscosity increase as by gelling, thus posing a problem in respect of storage stability.
On the other hand, there have been made a number of proposals of subjecting an aluminum substrate to anodic oxidation to form an anodized aluminum film thereon. However, the anodic oxidation requires special bath and technique which are time-consuming labored and costly.
Accordingly, a generic object of the present invention is to provide an electrophotographic photosensitive member having solved the above-mentioned problems of the prior art.
A more specific object of the present invention is to provide an electrophotographic photosensitive member including an intermediate layer which can be formed in a crack-free state inexpensively and without requiring a special technique by using a coating liquid of a good storage stability.
Another object of the present invention is to provide an electrophotographic photosensitive member including such an intermediate layer and capable of exhibiting excellent potential characteristic and image forming characteristic free from difficulties, such as lower image density or black spots and fog, over a variety of temperature and humidity environment conditions even at a smaller thickness of photosensitive layer.
Further objects of the present invention are to provide a process for producing such an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus including such an electrophotographic photosensitive member.
According to the present invention, there is provided an electrophotographic photosensitive member, comprising: a support, an intermediate layer and a photosensitive layer disposed in this order, wherein the intermediate layer comprises an at least 0.5 xcexcm-thick layer of aggregated particles having a composition represented by formula (1) below:
Al2O3.nH2Oxe2x80x83xe2x80x83(1), 
wherein n is a number of at least 0 representing a degree of hydration.
According to the present invention, there is provided a process for forming an electrophotographic photosensitive member, comprising the steps of:
applying onto a support a dispersion liquid containing particles having a composition represented by formula (1) below:
Al2O3.nH2Oxe2x80x83xe2x80x83(1), 
wherein n is a number of at least 0 representing a degree of hydration,
drying under heating the dispersion liquid on the support to aggregate the particles, thereby forming an intermediate layer having a thickness of at least 0.5 xcexcm, and
forming a photosensitive layer on the intermediate layer, thereby forming an electrophoto-graphic photosensitive member comprising the support, the intermediate layer and the photosensitive layer disposed in this order.
The present invention further provides a process cartridge and an electrophotographic apparatus including the above-mentioned electrophotographic photosensitive member.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.